package org.apache.lucene.index;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * A Term represents a word from text. This is the unit of search. It is
 * composed of two elements, the text of the word, as a string, and the name of
 * the field that the text occured in, an interned string.
 * 
 * Note that terms may represent more than words from text fields, but also
 * things like dates, email addresses, urls, etc.
 */

public final class Term implements Comparable, java.io.Serializable {
	String field;
	String text;

	/**
	 * Constructs a Term with the given field and text.
	 * <p>
	 * Note that a null field or null text value results in undefined behavior
	 * for most Lucene APIs that accept a Term parameter.
	 */
	public Term(String fld, String txt) {
		this(fld, txt, true);
	}

	Term(String fld, String txt, boolean intern) {
		field = intern ? fld.intern() : fld; // field names are interned
		text = txt; // unless already known to be
	}

	/**
	 * Returns the field of this term, an interned string. The field indicates
	 * the part of a document which this term came from.
	 */
	public final String field() {
		return field;
	}

	/**
	 * Returns the text of this term. In the case of words, this is simply the
	 * text of the word. In the case of dates and other types, this is an
	 * encoding of the object as a string.
	 */
	public final String text() {
		return text;
	}

	/**
	 * Optimized construction of new Terms by reusing same field as this Term -
	 * avoids field.intern() overhead
	 * 
	 * @param text
	 *            The text of the new term (field is implicitly same as this
	 *            Term instance)
	 * @return A new Term
	 */
	public Term createTerm(String text) {
		return new Term(field, text, false);
	}

	/**
	 * Compares two terms, returning true iff they have the same field and text.
	 */
	public final boolean equals(Object o) {
		if (o == this)
			return true;
		if (o == null)
			return false;
		if (!(o instanceof Term))
			return false;
		Term other = (Term) o;
		return field == other.field && text.equals(other.text);
	}

	/** Combines the hashCode() of the field and the text. */
	public final int hashCode() {
		return field.hashCode() + text.hashCode();
	}

	public int compareTo(Object other) {
		return compareTo((Term) other);
	}

	/**
	 * Compares two terms, returning a negative integer if this term belongs
	 * before the argument, zero if this term is equal to the argument, and a
	 * positive integer if this term belongs after the argument.
	 * 
	 * The ordering of terms is first by field, then by text.
	 */
	public final int compareTo(Term other) {
		if (field == other.field) // fields are interned
			return text.compareTo(other.text);
		else
			return field.compareTo(other.field);
	}

	/** Resets the field and text of a Term. */
	final void set(String fld, String txt) {
		field = fld;
		text = txt;
	}

	public final String toString() {
		return field + ":" + text;
	}

	private void readObject(java.io.ObjectInputStream in)
			throws java.io.IOException, ClassNotFoundException {
		in.defaultReadObject();
		field = field.intern();
	}
}
